| Re: WHILE NOT EOF(lun) wierdness under IDL 4.0.1 on Win NT [message #6393 is a reply to message #6392] |
Tue, 18 June 1996 00:00  |
Peter Mason
Messages: 145
Registered: June 1996
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Senior Member |
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On Mon, 17 Jun 1996, Joseph M. Zawodny wrote:
> I just ran across a very strange "feature" on IDL 4.0.1
> running on WIN-NT V3.51 and a Pentuim Pro. Basically the problem
> goes like this. I have a routine which reads from a previously
> opened file. It read in a structure and then 2 variable length
> records. The file is unformatted and access using READU. One of
> the fields in the structure contains the length of the arrays in
> the following records. If I call the routine (I called it READ_REC)
> manually, things are fine and I can read through the entire file
> without any problem. Similarly, I can put READ_REC in a FOR loop
> and work my way through the file. My intent has always been to
> use a WHILE NOT EOF(lun) construct with a READ_REC call within
> the WHILE block. This does not work! I can read the first two
> sets of three records correctly and on the third call, I read
> just the first three fields in the structure before hitting an EOF.
> IDL really thinks that it is at the end of the file and I cannot
> read any other data from the file. This is very reproducible.
>
> Has anyone else run into this? I certainly have not seen this
> happen on any of the UNIX versions of IDL I've used. Is this
> just another IDL 4 Windows "feature" (like the lack of support
> for 32 bit file systems - ie. long file names)?
Since Idl version 4, I found I have to use the /BINARY switch (and
/NOAUTOMODE, to be safe) on my OPEN calls under Windows, to get things to
work as expected.
I first noticed a problem while using READU/WRITEU with structures and a
binary file opened with /XDR - the reads and writes would sometimes
(unpredictably) work incorrectly - I sometimes couldn't read back into
the structure from which I had written (and it contained no strings :).
Using the above switches sorted it out.
I didn't notice problems like the one you described above (still can't
understand why the code would work from the command line and not from
within a routine), but try OPEN,/BINARY,/NOAUTOMODE - it's worth a shot.
Peter Mason
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